Steel products such as sheet, strip, plate, strand, coils of rod or wire or other manufactured pieces such as, for example, machined pieces and the like must frequently be chemically treated either in conjunction with other operations, such as heat treating or forming, or as a separate operation during manufacture of a finished product. The pickling of steel products to remove surface oxides is a typical example of such chemical treatment. Pickling involves the application to the steel of aqueous solutions containing corrosive chemicals, typically sulfuric acid or hydrochloric acid, broadly referred to hereafter as process materials. After such treatment is completed, the process materials must be removed from the steel surface quickly and efficiently in order to produce an acceptable product for sale or to prevent interference either by the process materials themselves or their residual corrosive effects with subsequent treatment steps.
It has been common practice to remove such process materials from steel workpieces by immersion or spray-rinsing of the steel. Sometimes the process materials have been removed by initially spraying the workpiece with fresh water and then dunking the workpiece in a tank of rinse liquid. This is commonly known as the spray and dunk system. Removal of the process materials has also frequently been accomplished in a multi-stage countercurrent rinsing apparatus. Such rinsing apparatus is generally composed of a series of interconnected rinsing stations. Each station is equipped with a collecting tank, at least one spray head, and pumping means connecting the tank to the spray head. In addition, the series of tanks are interconnected so that excess rinse liquid in one tank will flow into the next succeeding tank in the series. The flow of rinse liquid from tank to tank is countercurrent to the path of travel of the workpiece being cleaned through the rinsing apparatus. In operation, rinse liquid in each collecting tank is pumped from the tank to the associated spray head or heads of that tank where it is sprayed down on the moving steel workpiece from which it then falls back into the collecting tank. Any excess rinse liquid in the tank, which liquid contains a portion of the process material rinsed from the workpiece, overflows into the collecting tank in the next rinsing stage or station where it mixes with the liquid already in this succeeding tank. A portion of this mixture of liquids is then pumped to the spray heads at that rinse station and the process repeated. By using such an arrangement rinse liquid is conserved by virtue of the reuse of the successively more contaminated rinse water at each successive rinse station. The workpiece is rinsed initially with the most contaminated rinse liquid and ultimately in the last stage or station with the least contaminated solution or fresh rinse solution. This prior arrangement improves rinsing efficiency while using a minimum amount of rinse liquid. It also provides an easily controllable rinse process in which the rinse liquid throughout the system merely overflows from tank to tank and no complicated control system is necessary to coordinate the levels and rinse volumes in each successive rinse stage.
Despite the aforementioned benefits which arise from use of such a multi-stage rinser, the rinse arrangement as presently known still has certain drawbacks and there is a need for an even more efficient multi-stage rinser which will provide either equivalent cleanliness of the workpieces while using a smaller volume of fresh rinse liquid or an increased cleanliness of the workpieces when using an equivalent volume of fresh rinse liquid.
Herein the terms "preceding" and "succeeding" are used to refer to locations using the direction in which rinse liquid flows through a multi-stage rinse apparatus as a reference as opposed to the direction of movement of the workpiece through the apparatus. Thus, the term preceding refers to a location upstream of the rinse liquid flow, and the term succeeding refers to a location downstream of the rinse liquid flow with respect to any initially established location. For example, a first rinse station in which a workpiece is initially treated or rinsed will be called a succeeding rinse station, while a second rinse station in which the workpiece is then treated as it passes countercurrently with respect to the rinse liquid flow in the system will be called a preceding rinse station.